1. Field of the Invention
The present invention relates to the use of ultrasonic energy to heat biological tissues and fluids, and more specifically, to the use of hyperthermia potentiators, such as gas filled liposomes prepared by a vacuum drying gas instillation method, and/or gas filled liposomes substantially devoid of liquid in the interior thereof, in combination with ultrasound to facilitate the selective heating of the tissues and fluids.
2. Description of the Prior Art
The usefulness of heat to treat various inflammatory and arthritic conditions has long been known. The use of ultrasound to generate such heat for these as well as other therapeutic purposes, such as in, for example, the treatment of tumors has, however, been a fairly recent development.
Where the treatment of inflammation and arthritis is concerned, the use of the ultrasound induced heat serves to increase blood flow to the affected regions, resulting in various beneficial effects. Moreover, when ultrasonic energy is delivered to a tumor, the temperature of the tumorous tissue rises, generally at a higher rate than in normal tissue. As this temperature reaches above about 43.degree. C., the tumorous cells begin to die and, if all goes well, the tumor eventually disappears. Ultrasound induced heat treatment of biological tissues and fluids is known in the art as hyperthermic ultrasound.
The non-invasive nature of the hyperthermia ultrasound technique is one of its benefits. Nonetheless, in employing hyperthermic ultrasound, certain precautions must be taken. Specifically, one must be careful to focus the ultrasound energy on only the areas to be treated, in an attempt to avoid heat-induced damage to the surrounding, non-targeted, tissues. In the treatment of tumors, for example, when temperatures exceeding about 43.degree. C. are reached, damage to the surrounding normal tissue is of particular concern. This concern with over heating the non-target tissues thus places limits on the use of hyperthermic ultrasound. Such therapeutic treatments would clearly be more effective and more widely employed if a way of targeting the desired tissues and fluids, and of maximizing the heat generated in those targeted tissues, could be devised.
The present invention is directed toward improving the effectiveness and utility of hyperthermic ultrasound by providing agents capable of promoting the selective heating of targeted tissues and body fluids.